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Continental Rifting and Porphyry-Molybdenum Occurrences in the Oslo Region, Norway

1983; Elsevier BV; Linguagem: Inglês

10.1016/b978-0-444-42198-2.50039-0

2212-0734

H.K Schønwandt, Jon Steen Petersen,

High-pressure geophysics and materials

Schönwandt, H.K. and Petersen, J.S., 1983. Continental rifting and porphyry-molybdenum occurrences in the Oslo region, Norway. In: P. Morgan and B.H. Baker (Editors), Processes of Continental Rifting. Tectonophysics, 94: 609–631. The overall structure of the Oslo rift-system can be viewed as the result of interference between a N-S trending Permian fault system and a regional NE-SW trending, Precambrian shear-zone. The rift system comprises four mutually opposed horst and graben structures in a centrosymmetrical arrangement. Igneous activity occurred only in two en echelon segments, both of which possess a notable symmetric distribution of rocks and structures around the central axis of the rift system. The axial zone is occupied by Cambro-Silurian sediments which have been intruded by major granite bodies. Extensive lava-plateaus occur on each side of this axial zone. The adjacent zones contain the most prominent cauldrons of province. Further away from the axis follows a zone of batholitic intrusions, emplaced as composite diapirs and plutonic ring complexes. Hornfelsed sediments and volcanics in narrow bands occur at the lateral borders of the province, possibly preserved as the result of marginal tectonics associated with batholith emplacement. The formation of the Oslo Rift system apparently reflects a passive continental rifting which was gradually succeeded by considerable igneous activity. Important porphyry-molybdenum mineralization in the Oslo region is associated with shallow level magmatism in the Glitrevann and Hurdal areas. The porphyry-Mo mineralization in these prospects have several evolutionary features in common: (1) an initial period of effusive eruptions of pyroclastic flows followed by (2) the formation of large-scale ring structures, partly accompanied by peripheral syenite-granite intrusions; (3) the emplacement of a multiple intrusive, central stock of sub-alkaline granite composition which is terminated by (4) the injection of a highly differentiated aplogranite-granophyre, closely associated with the development of the mineralizing hydrothermal porphyry system. Molybdenum mineralization of the Oslo province is closely associated with highly differentiated alkali granites which possess striking similarities to Mo-related granites of the Colorado Mo-province and evolved Rapakivi- or A-type granites, usually considered to be typically associated with bimodal magmatism of crustal extension and continental rifts. The discovery of significant porphyry-Mo mineralization in the Oslo rift associated with Permian igneous rocks draws attention to the possible economic potential of rift structures elsewhere.